1. Field of the Invention
The present invention relates to a wireless communication device and a wireless communication method.
2. Description of the Related Art
With improvement of the communication speed and the usability, wireless communication techniques have been used widely in various situations and locations, for example, in the houses, offices, and schools. Wireless communication devices have been proposed to have various functions including broadband router function as well as general access point function (for example, JP-A-No. 2007-325041).
With advance of the wireless communication technology, there is a movement to extend the available range of carrier waves for wireless communication. This movement gives permission for the use of a 5 GHz frequency band, in addition to the conventionally used 2.4 GHz frequency band. In Japan, a frequency band of 5.25 to 5.35 GHz (corresponding to a W53 frequency band with four channels 52/56/60/64) was permitted for the indoor application in 2005. A W56 frequency band (5.470˜5.725 GHz) with eleven channels 100/104/108/112/116/120/124/128/132/136/140 was permitted for both the indoor application and the outdoor application in 2007.
The W53 and W56 frequency bands are generally used by various radars including moving radars, such as radars on boats and ships, aircraft radars, and radars for military purposes, and stationary radars, such as weather radars. There is accordingly a possibility of interference with radio signals used by such equipment. For the purpose of adequate assignment, the wireless communication devices are obliged to avoid interference by DFS (Dynamic Frequency Selection) technique. The required DFS functions include CAC (Channel Availability Check) that monitors a channel for one minute prior to an actual use of the channel and gives permission for starting the actual use of the channel only after confirmation of non-detection of radar/radio signals at the channel and ISM (In-Service Monitoring) that continuously monitors detection of radar/radio signals during the use of the channel. In the event of detection of radar/radio signals at a current active channel, an adequate interference-avoiding measure is required to promptly stop the use of the current active channel within 10 seconds. Avoiding the interference by DFS is required in the countries such as China and Europe in which the use of the W53 or W56 frequency band is permitted. These DFS functions and other relevant functions are essential for access points and other devices and equipment workable as a base station in wireless communication.
The interference-avoiding measure by the DFS technique taken in response to detection of radar/radio signals at a current active channel in a frequency band means that the radar/radio signals have the priority of using the frequency band. Data transmission in a wireless LAN may thus be interrupted in the case of detection of radar/radio signals. When radar/radio signals are detected at a current active channel for the wireless LAN, the current active channel becomes unusable. During a CAC of a newly allocated channel, the newly allocated channel is not usable for the wireless communication. Even when no radar/radio signals are detected at the newly allocated channel, the wireless LAN is interrupted for one minute.
This problem is not characteristic of the communication in the wireless LAN but is also found in communication between multiple access points, for example, communication in a WDS mode.